When the optional argument is #f (the default), this function
returns the offset of the main screen’s origin from the
top-left of the physical screen. Under X and Windows, the result is
always 0 and 0; under Mac OS X, the result is
0 and the height of the menu bar.

When the optional argument is true, this function returns the amount
space at the left and top of the main screen that is occupied by the
task bar (Windows) or menu bar and dock (Mac OS X). Under X, the
result is always 0 and 0.

This font is the default for group-box-panel% objects, and it is
a suitable for controls in a floating window and other contexts that
need smaller controls.

Under Windows, this font is the same size as
normal-control-font, since the Windows control font is
already relatively small. Under X and Mac OS X, this font is slightly
smaller than normal-control-font.